What causes a SPN 7994 code?

SPN 7994 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a SPN 7994 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 7994 active.

How do I fix SPN 7994?

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

J1939 SPN

SPN 7994

Cummins fault code 7994

What it means

Aftertreatment 1 Outlet NOx Sensor - Abnormal Update Rate. This indicates the Engine Control Module (ECM) has lost communication with the downstream (SCR outlet) NOx sensor via the J1939 data link.